class Queue<T> {
  private data = [];
  push(item: T) {
    // this指向实例化对象queue => Queue{ data: [] }
    return this.data.push(item);
  }
  pop() {
    return this.data.shift();
  }
}

const queue = new Queue<number>();
queue.push(1);
// console.log(queue.pop().toFixed());